Epidemiology and incidence of oral squamous cell carcinoma in the Iraqi population over 5 years (2014–2018)

Abstract Background Oral squamous cell carcinoma is one of the most common and life‐threatening neoplasms worldwide, and is responsible for approximately 90% of all oral malignancies. Aim This study was aimed at providing updated information on oral squamous cell carcinoma in all Iraqi governorates for the 5‐year period from 2014 to 2018, including the annual incidence and demographic variables. Materials and Methods The total number of oral squamous cell carcinoma cases in Iraq, along with associated demographic information (age, sex, and site), for the 5‐year period from 2014 to 2018 was obtained. The statistical analysis consisted of descriptive analysis, including frequency, percentage, and mean ± standard deviation. A χ 2 test was performed to compare frequencies between male and female patients, among age groups, and among different OSCC sites. The χ 2 test was also used to assess the association of each OSCC site with age and sex. The significance threshold was set at p < 0.05, and the confidence interval was set at 95%. The incidence rate of oral squamous cell carcinoma for each year was calculated by dividing the number of OSCC cases per year by the population of Iraq, then multiplying the result by 100,000. Results A total of 722 cases were recorded. Statistically, oral squamous cell carcinoma was found to be more prevalent in males and individuals over 40 years of age. The tongue was the most common site of occurrence. Lip squamous cell carcinoma cases were high in males. The incidence rate of oral squamous cell carcinoma was estimated to be 0.4 per 100,000 people. Conclusion Males and older people are at relatively higher risk of developing oral cancer. The tongue is the most affected site, but any site in the oral cavity may be involved. Further exploration of the causes of oral malignancy in Iraq is necessary to improve prevention strategies.


| INTRODUCTION
Oral squamous cell carcinoma (OSCC), a malignant neoplasm of the oral cavity, is associated with high morbidity and mortality. 1 OSCC is one of the most frequent malignancies worldwide, and it accounts for 90% of all oral cavity cancers. 2 Multiple risk factors have been documented to be associated with OSCC, including smoking, alcohol intake, infection, sun exposure, poor oral hygiene, chronic irritability, and genetic disorders. 3,4 Many studies have indicated that males are more commonly affected by OSCC than females, and older people are believed to be at the highest risk of developing OSCC. 5,6 OSCC may affect the mucosa of all anatomical sites of the oral cavity. 7 Clinically, OSCC usually manifests as ulcers, exophytic tumors, or patches of leukioplakia or erythoplakia. 8 The prognosis of OSCC is affected by the stage and location of the cancer, and the overall health of the patient. The 5-year survival rate for people with earlystage OSCC is approximately 80%-90%, but is only approximately 30%-50% for people with advanced-stage OSCC. 9,10 Epidemiological studies are important for understanding the prevalence, demographic characteristics, and incidence of cancer, as well as the risk factors for specific types of cancer. In addition, epidemiological studies enable evaluation of the effectiveness of cancer control strategies. Incidence refers to the number of new cases of cancer in a specific period.
The outcomes of epidemiological studies can be used to guide the development and implementation of cancer prevention and control programs. 11,12 The last nation-wide epidemiological study on OSCC in Iraq was for the period from 2001 to 2013, but that study did not cover all of Iraq, because the Kurdistan region was not included. 13 Therefore, the objectives of the present study were to provide updated information on OSCC in all Iraqi governorates for 5 years (2014-2018), including the annual incidence and demographic variables (age, sex, and site).

| MATERIALS AND METHODS
The current study was a retrospective cohort study conducted in Iraq Planning. 16 The sexes were classified as male and female, and the age was calculated by year and divided into groups >40 and ≤40 years of age.
The locations of OSCC cases were classified as buccal mucosa, floor of the mouth, gingiva (gingiva and retromolar pad), lips (upper and lower lips), unspecified sites, palate (hard and soft palate), and tongue.

| STATISTICAL ANALYSIS
Statistical analysis was conducted in SPSS software (version 14) and included descriptive analysis and inferential analysis. The descriptive analysis included the frequency, percentage, and mean ± standard deviation (SD). The inferential analysis first included χ 2 tests to compare frequencies between males and females, among age groups, and among the sites of OSCC.
Subsequently, the association of each site of OSCC with age and sex was tested. Significance was established at p < 0.05, and the confidence intervals were set to 95%.

| RESULTS
The total number of OSCC cases in Iraq during the 5-year period (2014-2018) was 722. The number of males (389) was significantly higher than that of females (333), and the male-to-female ratio was 1.2:1. The prevalence of OSCC was significantly higher among individuals older than 40 years (p ˂ 0.00). The most common sites for OSCC were the tongue, followed by the lips. Gingiva was the least frequent site affected by OSCC. Table 1 describes the distribution of sexes, age groups, and cancer sites. Table 2

| DISCUSSION
The results of the current study indicated a higher incidence of OSCC among males than females. This finding is in agreement with those from prior studies. [18][19][20] A plausible explanation for this result may be that the documented prevalence of smoking and alcohol consumption in Iraq and other countries is higher among men than women. [21][22][23][24] Furthermore, the tendency for men to have occupations to located outdoors increases their exposure to carcinogenic elements, such as ultraviolet radiation and human papilloma virus. 25,26 The present investigation indicated that the male-to-female ratio was 1  27 Previous epidemiological studies conducted in other countries, such as India, 28 Brazil, 29 Taiwan, 30 México, 31 Qatar, 15 and Jordan, 32 have also reported a high prevalence of OSCC in males.
Most cases of OSCC were identified in individuals older than 40 years, and the average patient age was in the fifth decade, in concordance with the results of prior investigations conducted in Iraq, 33 Pakistan, 34 Mexico, 31 Iran, 35 and Brazil. 18 Aging is considered to contribute to the development of OSCC, owing to multiple interrelated factors. As individuals advance in years, they become more susceptible to the risk factors associated with OSCC, such as exposure to tobacco and alcohol use. 36 Furthermore, the decline in the body's natural defense mechanisms with age increases the vulnerability of older individuals to cancer development. 37 Moreover, the ability of the body  38 In addition, older individuals tend to have insufficient awareness of oral health, which is a risk factor for oral cancer. 39 Consequently, the incidence of OSCC increases with age, thus making age a critical factor in OSCC development.
The tongue was found to be the most common site of OSCC in the present study, in agreement with previous research conducted in Iraq and other parts of the world. 29,40 The high incidence rate of tongue cancer is explained by the tongue's being subjected to repeated friction and trauma caused by sharp or misaligned teeth or improperly designed dental prostheses. Additionally, the tongue is located near areas that are often exposed to carcinogens, such as tobacco and alcohol, thereby increasing the risk of OSCC. 41 In contrast, a previous study in Taiwan has indicated that the buccal mucosa is a common site of squamous cell carcinoma. This finding has been attributed to the habit of betel quid chewing. 42 The present study determined that the average incidence of OSCC over the 5-year period of 2014-2018 was 0.4 per 100,000 people. This result is consistent with the findings of Shahrour and colleagues, who have reported an incidence of OSCC in Syria of 0.5 per 100,000 people. 43 However, the observed incidence of OSCC in this study is lower than those reported in China, 44 Japan, 45

CONFLICT OF INTEREST STATEMENT
The authors declare no conflict of interest.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.

ETHICS STATEMENT
Ethical approval for this study was obtained in accordance with the Declaration of Helsinki.

TRANSPARENCY STATEMENT
The lead author Muhanad L. Alshami